Stretch-wrap forming machine



April 27, 1954 u w. G. WHEELER ET AL 2,676,638

` STRETCH-WRAP FORMING MACHINE Filed July 26, 1952 4 sheets-Sheet 1 Gttorneg vkAPI-fl 27, 1954 w. G. WHEELER ET AL 2,576,638

STRETCHEWRAP FORMING MACHINE Filed July 26, 1952 4 Sheets-Sheet 2 m i Ww u l (ttorneg -ma r n E FILM! awww April 27, 1954 w. G. WHEELER ET AL 2,676,638

STRETCH-WRAP FORMING -MACINE Filed July 2e, 1952 4 Ysheets-sheet s I E Lglxzventors WALTER 6. WHE

0A l//D 6'. KRAMER Gttorneg April 27, 1954 w, G, WHEELER ET AL STRETCH-WRAP FQRMING MACHINE 4 Sheets-Sheet 4 Filed July 26, 1952 Patented Apr. 27, 1954 UNITED STATES earner erics- 2,676,63sw l A STRETCH-WRAP FORMING MACHINE Walter G. Wheeler, Los Angeles, and David` C.

Kramer, Redondo Beach, Calif., assigncrs to Richard Seifried; Playa del Bey, Calif. l'

Application July 26, 1952, Serial No. 301,024

(.Cl. l53-32) 12 Claims. l This invention relates to a machine for form-r ing, by stretching and wrapping, sheets of tapered thickness and of initial rectangular or trapezoidal form.

. An object of the present invention is to provide a machineto exert an initial stretch force on a sheet as indicated, to Wrap the sheet around a die to a desired angular degree up to a maximum wrapping angle of 180 while the sheet is stretched to, its elasticlimit, and, nally, subjecting the sheet so wrapped to a nal stretchv force by applying additional tension thereon to set the .sheet against spring-back.

Another object of the invention is to provide amachine that, in applying initial stretch, ap-

plies a` stretch-leveling force 'to remove wrinkles,r Y

bulges, etc., from commercial sheets so that they are quite ilat and level, being stretched Yiiatby such an operation.y f L VA further objectof the invention is to provide a machine 'for thepurpose indicated'and to Lemploy hydraulic'units to control andcreate the stretching, wrapping andY setting kforcesin said units. Y

vA still further object of theinvention is to provide an hydraulic machine of the nature indicated in which plural banks of hydraulically operated mechanisms 'areprovidedfor exerting different degrees of stretch force on a sheet being stretchwrapped and to provide means to exert-,on an intermediate portion oi the sheet the average ofthe forces exertedron the end portions so that the Ysheet is uniformly stretched,A particularly when stretched over a die of conical form. A

',The invention also has for its objects Vto 'provide, such means that are positive in operation,

convenient in use, easily installed ina working position `and easily disconnected .therefrom," economical of manufacture, relatively simple,v

and of general superiority and serviceability. The invention also comprises novel details of construction and novel combinations and ar lowing descriptionl merely describes yone embodifment of the present inventior1,; which is given t by Way of illustration4 or example only.` c

nIn the drawings, like reference characters` designate similar parts in the several views. i'

,llig.V A 1. isga .top plan view of a st re t :l 1wrapvr `forming machine according to the present in-vv vention.

Fig. 2 is a online 2-2of Fig. nll. E.

longitudinal sectional view as taken.

y Y. ri Y J 5.5

Fig. 2a is an enlarged fragmentary cross-sectional view as taken on line 2er-2a of Fig. 2.

Fig. 3 isr a cross-sectional view as taken on line 3 3 of Fig. 1.

Figs. 4 and-5 are enlarged cross-sectional views of details of construction.

Fig. 6 is an edge View of a taper-sectioned sheet adapted to be handled by the present machine. i

Fig. 'l is a semi-diagrammatic view oi one side of one bank of the present machine, showing control means therefor.

Fig. 8 is a diagrammatic view showing the manner of application of dividing valve means whereby the hydraulic units of the middley of three banks of such units is controlled by the units of the two outer or end banks.

Fig. 9 shows` aseries of fragmentary detail views of thediferent positions of control switch f means. employed in the invention.

to reach the elastic'limit of, forinstance, a sheet of aluminum alloy of substantial thickness, said machine, in practice1 vis quite large and powerful. VThe drawings show a machine, as at presentV contemplatedjto a greatly reduced scale. Actuallysaid machine is about thirty-one feet high with the portions above the pit about ten feet high, and about sixty-six feet across as in Fig. 2. A machine of this size is intended to handle a maximum sheet that is inch thick, twenty vfeet long, and thirteen feet wide.A The sheet is designated 9 in the drawings.

While the machine components may be mounted -in a fabricated frame, the same, as shown, vare preferably mounted on ther concrete liningV l@ of a'pit Ii. The machine that is illustrated. comprises', generally, die means I2 iixediy positioned transversely above the pit H centrally of its long dimension, sheet-tensioning or lstretching means i3 mounted on the pit lining i0 on opposite sides of the die means, controlmeans' I4 carried by each tensioning means,

asheet-gripping jaw l5 carried by each control means, javv-positioning meansle to control vthe f position of thejaws l5 and to return them to sheet-gripping Vposition after a wrapping oper'-V ation, actuatingmeans il :for wrapping sheet 9 around die means l2 Vandfor imparting a finalf setto Ythe wrapped sheet, and means i8, to porsitionvthe actuating means to `obtain the most effective line of pull on the wrapped sheet by the actuating means.

It will be noted that the machine is symmetrical with die means I2 at the middle thereof and that the means I3, I4, I5, I6, I1 and I8, on one side of the die means, are identical to said means on the opposite side. Therefore, the following description of one each of said means will serve to describe the counterpart on the opposite side.

Die means I 2 comprises a die support platen 20 iiXedly mounted atop a transverse structural member 2| that has its ends embedded in or supported by the opposite walls 22 of concrete lining YIii. Die platen 20 mounts a die 23 formed according to the shape to which a sheet 9 is to be bent. The die shown is tapered although the same may be of uniform width as will hereinafter be seen.

Sheet-tensioning means I3 comprises a bracket 24 affixed atop an end Wall 25 of lining I0, an hydraulic cylinder 26 having therein a piston 2'! provided with a rod or stem 28, and aset of gimbal pivots 29 mounting said cylinder in said bracket. Said pivots 23 comprisea transverse horizontal pivot 3E] mounting a ring 3| on bracket 24 and a pivot 32, perpendicular to pivot 30, mounting a collar 33 in ring 3I and affixed to cylinder 2G. Pivot 3U is parallel to the longitudinal dimension of die 23. Therefore, cylinder 2&5 is mounted for pivotal movement in a vertical plane that is transverse to said die. Pivot 32, being perpendicular to pivot 3U, mounts said cylinder for movement in the plane of die 23 or in a plane extending at an angle through pivot 3d. pivots 2S, has limited universal movement in its mounting bracket 24. This cylinder, as are the other cylinders hereinafter described, is provided with connections to a source of hydraulic fluid to project or retract piston rod 24 as desired. Such connections are not shown because of their conventionality.

The projecting end of piston rod 28 is provided with fork-like fitting 311v that has forwardly directed spaced ears 35 that mount control means iil, and downwardly directed spaced ears 35 that connect to actuating means I'I.-

Control means i4 comprises an hydraulic cyl-V inderv it? carried by a transverse pivot 38 between ears 35 of fitting 34, a piston 33 in said cylinder, and a piston rod 49 on said piston and extending forwardly from cylinder 38. A clevis 4I is provided on the projecting end of rod 40.

A vertical pivot 42 connects said clevis to sheetgripping jaw I in a manner that allows the latter to assume various angular positions relative to the plane of control means I4.

As shown in Figs. i and 3, the components of the machine are provided in plural banks. Three such banks are shown, but the number may be increased or decreased, as desired. However, on each side oi' die 23 there is'provided but one sheet-gripping jaw I5, the same being connected by pivots 42 to the different banks that are provided. Thus, each bank, by independent action, innuences the movement of and the force applied to said jaw.

Jaw I5 comprises an elongated bar 43 which is provided in its forward face with a longitudinal slot 44. Within said slot is preferably provided a plurality of grippers 45.which are individually operated to grip sheets 9 of uniform thickness or sheets of tapering thickness. These grippers are not shown indetail because they generallyV comprise conventional vise jaws nthat in other words, cylinder 23 on gimbal 4 may be moved together or apart by suitable means, for instance hydraulic cylinder means.

J aw-positioning mea-ns I is provided for moving the jaw means I5 to a position receptive of a lateral edge of sheet S, i. e., to a loading position. Said means comprises an extension of pivot 38, which is afxed to cylinder 3l', an arm 46 iiXedly mounted on said extension, and an hydraulic cylinder di pivotally carried by ntting 3d and having a piston therein that is provided with a piston rod 48 connected to the end of said arm-4E. It will be apparent from Fig. 1 that jaw means I5 and control means ill can be angularly adjusted on pivot 38, relative to the axis of piston rod 28, to direct the sheet-receiving slot 44 as desired.

The actuating means I`I for wrapping the sheet 3 around die 23 comprises an actuating hydraulic cylinder 49 having a piston 5i) therein, and afpiston rod 5I extending upwardly from said cylinder." The means I'i has a generally vertical disposition in pit I.A An eye 52 extends from the lower endofv 'cylinder 49,' and a clevis 53 is'provided on the upper end of rod 5I. Said clevis and the ears 36 of iittng 34 are connected by a universal knuckle" 54 by lmeans or mutually transverse pivots 55 and 56. Eye 52 has a uni'- versal gimbal mount that comprises a pivot 5i connecting said eye to a ring 58, and a transverse pivot SQ that connects said ring to opposite slide blocks Eil. The latter are mounted in slideways tl'provided in support walls or brackets 62 longitudinally disposed on the bottomof pit i I.

' Said latter gimbal mount provides for universal angular disposition of actuating means II, theknuckl'e 54 and its pivots 53 and 56 allowing such angular movement with respect to the movements of tensioning means I3.'

The means I8 effects the general disposition of means I'I relative to die 23. As shown, said means comprises an hydraulic cylinder 63, mounted on a bracket 64 in the bottom of the pit I I, and provided with a piston 65 from which extends a piston rod 66. The latter, through a connection 61, connects to slide blocks 6U. It will be clear that the means I'I is disposed as desired by suitable projection or retraction of rod Et to slide blocks B in their ways 6I.

Operation using a parallel-sided. die

After a parallel-sided die 23 is formed, the same is placed on and secured to die platen 20. The positioning means I8 on both'sides are used to move the pivots 5S of actuating means I1, along slideways tI, so that jaws I5 are directly beneath the oppositeedges ofthe die.` This position is shown by the dot-dash lines of Fig. 2. This initial set-up procedure is important because it becomes possible for the nal setting pull on a sheet to be applied tangent to the die, thereby eliminating any tendency of the jaws to pull away from the die. Y

From this initial set-up position, the means I3,l I6 and I'i are manipulated to bring the'jaws I5 to a horizontal position and into gripping engagement with the opposite lateral edges of a sheet 9 lowered into position on die 23. The three cylinder means are controlled as desired to align the jaws with the top of the die and also move them toward each other to eifect engagement of the sheet edges in slots 44'. In this manner, they sheet is gripped without tension, as shown by the full-line position of the parts in Fig. 2,

-Now,'pressure fluid is admitted into the forward ends of cylinders 26 togexert va tension force on sheet S until the elastic limit of the material of said sheet isv reached. During this application of force by cylinders 26, the control means Ui. are employed to insure the correct degree of tension force on thesheet by admitting hydraulic pressure into cylinders 31 to retract pistons 3. Thus, the vmeans i3 is used for approximate application of force and .the means i4 for a finer and more controlled application.

With the sheet stretched to its elastic limit to insure that the metal flows .smoothly and evenly around the die, the wrapping ,cycle is started. The actuating means I1 are operated by admit'- ting pressure iluid into the upperV ends of cylinders 49 to retract pistons 50 and exert a pulldown forceon fittings 34. This application of force causes the means I3 and I4 to change their relative angular position on pivot. 38.and both said means to change angular position relative to the means il on pivot 55. As the piston rods continue to retract, the gripping jaws I5 are swung in curved paths. around the sides of die 23. Since the control means land jaws I5 are free to pivot as above, they at all times remain inthe line of pull exerted by means Il, l Y

As the pull-down Wrapping force of actuating means lisis applied, the tensioning means I3 are controlled to pay out or decrease their force. By balancing the decreasing force of means I34 with the increasing force of means il' a constant forceis continuously applied on sheet 9. The control .means irl controls the rate of the decreasing force of means i3.

This action can be stopped at any intermediate stage when the oppositelateral edges of sheet 9. assume angularr` positions asV desired. Such lintermediate stage is when the'sheet edges dene an included angle between 180 and' more thanil When a zero angleY is desired, i. e., when the lateral edges of the sheetr are brought into parallelism, the wrapping cycle is continued until means I1 pulls straight down. At this stage, also shown by the dot-dash lines of Fig. 2, all of the pullingforce has been transferred from the tensionng means i3 to the actuating lmeans Il. j

After .the desired amount of wrap has been attained, the actuating means il .apply an additional general force and the controlV means I4 apply a control for said force to impart an elongating final setting pullon the sheet. Thisiinal stretch minimizes spring-back and, therefore, insures retention of the formed shape of the sheet.

At this time, grippers i5 are released and the formed sheet is removed from the die. Since the actuating means il iinishesits cycle of operation in the same position it was initially'set, it is only necessary to return'the jaws i5 to their thereof is parallel to any other position and all positions are parallel to the die.V VThe ability of the machine to form conically shaped or bent sheets depends on the ability of said jaws to rotate, tilt or oscillate in two planes as well as, to move parallel to a conical die. In other words, the jaws must be able to oscilalte in a horizontal plane and rotate in a vertical plane simultaneously, and such oscillation and rotation must be compounded in any desired proportional degree.

As above stated, the jaws must be free to move in a path always parallel to the slant height of a conical die for the reason that the same has no diameter that is perpendicular tothe edge. Otherwise, the sheet will slide over the die during wrapping.

The initial set-up is shown in Fig. 1, wherein it is seen that the jaws I5 are horizontally aligned but non-parallel. The cycle of operation is performed, as described, although the different banks perform to move the jaws from said non-parallel horizontal position to a position, after wrapping, with the jaws beneath and aligned with the opposite non-parallel sides of the die and still horizontal although-rotated through 90, as

before.

It 4will be realized that the dierent hydraulic components of the different banks thereof are controlled to exert force on and move jaws I5 in the desired compound path according'to the degree of taper of die 23.

The present machine can also handle tapersectionedsheets of non-uniform width, as shown in Fig. 5. The pull on a taper-sectionedk sheetV must vary as the cross-sectional area varies, in

'Y cycle is instituted, as before described. Thus,

from an initial iiatrpattern section that is ta- Y pered, the wrapped sheet is provided either with initialsheet-gripping position for a repetition;of

the operation on a subsequent sheet, the means I6 being employed to return said jaws to aligned position. y

While the foregoing describes a symmetrical wrapping operation with both edges of the sheet wrapped the same'amount, it will be evident that only one side cf the sheet may be wrapped while the other'is held in tension, or one side' may be wrapped to a greater angular degree than the other. Needless vto say, itis only necessary 'to maintain equalpulling forcesjon both sides of the sheet so that the latter does notshift relay tiveito the die.

Operation using azttapered or conicaldaV In the'previously-describedoperation, the jaws I5 describe a Vcurved Vpathin which Vany positionv a lesser tapered cross-section or with a uniform cross-section, as desired. t

Since thelength of jaws i5 can be made to at least equal the kover-all rdimension of the machine from `front, tobaclr, two such machines may be installed side-by-side so as to handle sheets greater `than twenty feet iii-length. Infact, the

number of banks may be varied as desired.

'While it is conceivable that the above-described machine may have, itsvarious hydraulic components controlled byinanual or like operationof Valves admitting or releasing hydraulic pressure thereinto, a more practical means for controlling the tensioning means I3, control means I4, and actuating means I'i is disclosed in Fig. 7, wherein the line lil represents the center on which' die 23 isV positioned and the mechanism shown on the right of vsaid line is duplicated on the left thereof.

In a three-baril; machine as illustrated in Figs. l', 2v and 3, the means shown in Fig. 7 would be applied to the two outer banksand, while also applied to the vmiddle bank, the latter would also include the pressure-averaging means shown in Fig. 8j

MReferring now more particularlyto lf"igs."lv andV 9, hydraulicv pressure .fluid is ladmitted into cylinder 26 of mea-ns Irlthiougha ),:iipe'll Which the pressure from a suitable pump or other source, connected to pipe 12, is controlled by a pressure relief valve 13. An electric motor 14 is connected to valve 13 to adjust the relief pressure. A reversing motor is used, the same increasing or decreasing the pressure in pipe 1l according to the direction in which it is rotated. Said valve 13 exhausts through a. pipe 15.

Pipe 1I is connected to cylinder 26 on the end thereof that will result in retraction of piston rod 28 when pressure iiuid is admitted through said pipe.

Hydraulic pressure fluid is admitted into cylinder 31 of control means I4 through a pipe 16 in which a continuously operating pump 11 is employed to provide the pressure. Said pipe 16 is connected to cylinder 31 on the end thereof that will result in retraction of piston rod 48 and jaw l5 on the end of the latter.

An electric motor 18 operates to control the pressure-setting of pump 11. As said motor continues to operate, the pressure in pipe 16 increases. A fluid bleeder 19 is provided and normally is set to bleed the pressure in relation to the pressure in cylinder 26.

A suitable source of pressure fluid may .be connected to cylinder 49 through a pipe 88 connected on the end of said cylinder that will result in a downward or' retractive movement of stem 5I.

Motor 14 is driven in one direction by an electric circuit 8| under control of a normally-open limit switch 82 and in the reverse direction by an electric circuit 83 under control of a normally-open limit switch 84. Both said limit switches are carried by rod 48. Switch 82 closes upon retractive movement of rod 49 by a cam actuator 85 mounted on cylinder 31, and switch 84 closes upon movement of cylinder 31 away from jaw I5 by a cam actuator 86 also mounted on said cylinder. The switches 82 and 64 may be carried by cylinder 31, in which case actuators 85 and 86 are mounted on rod 40.

To start motor 18, any suitable push-button control may be provided. Said motor 18 is also controlled by piston rod 28 as pressure in cylinder 26 is increased. A gear rack 81 carried by said rod 28 is engaged to rotate a pinion gear 68 mounted on a bracket 89 ixedly carried by cylinder 26. A grooved interrupter wheel 89 is rotated by gear 88 and intermittently controls a normally-open limit switch 9i. An electric circuit 92 interconnects switch 9| and motor 18, and an impulse counter 93, set for a predetermined number of impulses created by the makeand-break action of switch SI, acts to open the circuit 92 and stop motor 18.

Said impulse counter 93, and such other electrical controls as may be employed in the machine, are advantageously grouped in a control console 94 physically remote from the machine but placed where an operator may control the operation of the latter.

Operation of controls At the start of the initial stretching operation, motor 18 is set in operation to change the pressure setting of pump 11 to increase the pressure in cylinder 31 and retract rod 48. As rod 48 starts to retract from the rst position of Fig. 9 to the second position, limit switch 82 is closed by actuator 85 to close circuit 8l to motor 14 and drive said motor in a direction to set relief valve 13 to increase pressure in cylinder 26. Thus, piston rod 28 starts to retract. l Y Y Retraction of rod 28 sets up rotation of interruptor wheel 90 to intermittently close normally-open limit switch 9| and, thereby, create a series of electrical impulses, through circuit 92, in impulse counter 93. When the predetermined number of impulses has been reached in said counter, the circuit to motor 18 is broken causing said motor to stop. The pressure in cylinder 31 will remain at the pressure setting of'pump 11 which continues to operate.

During this time, the rod 28 is continuing to retract and the pressure in cylinder 26 is continuing to increase. When the force on rod 28 is greater than the force in cylinder 31, the latter cylinder will move in a direction away from the center of the machine as exemplified by line 10, because the iluid bleeder 19 will allow such movement of cylinder 31 relative to rod 49 and sheet 9. The pressure in cylinder 3l will be maintained, however, by pump 11.

When the cylinder 31 is thus moved, as shown in the-third position of Fig. 9, actuator moves withv it to open limit switch 82, open circuit 8i, and stop operation of motor 14. Whatever pressure the valve 13 has been set for during the mentioned operation of said motor is now maintained in cylinder 2B. In this way, the sheet 9 is placed under stretching tension and the same is maintained preparatory to starting the sheet-wrap ping operation.

rIhe wrapping operation is accomplished by means i1. Pressure fluid is introduced through pipe 88 to retract rod 5l and, thereby, exert a downward pull on cylinder 31 through pivot 38. Since the pressure in control cylinder 31 is maintained constant by pump 11 according to pressure setting of said pump, there will be no additive force on rod 46 to create additional stretch force on lsheet 9 as cylinder 31 is pulled by rod 5i In substantially the same way that bleeder 19 allowed cylinder 31 to move under pull of rod 28 without change in the set pressure in said cylinder, said bleeder now allows cylinder 31 to move under pull of rod 5i, again without change of set pressure in said cylinder. As shown in the last position of Fig. 9, this move-ment of cylinder 31 closes limit switch 84 when cam actuator 86 is moved with said cylinder. Thus,4 the reverse circuit 83 for motor 'i4 is energized to reduce the pressure setting of relief valve 13. The pressure in cylinder 26 will, therefore, decrease.

t will be clear that as the rod 5i continues to exert its downward force, piston rod 28 projects or pays out by reason of said decreasing pressure in cylinder 26. It will be recalled that the cylinder 3'? is being supplied with a constant, set pressure. Consequently, as the pressure in cylinder 2li decreases rod 28 and cylinder 3? move back to the third position of Fig. 9, wherein switch 84 is open and the electric circuitB is broken to motor 1d. At this point, the pressure in cyln inder l26 stops decreasing and is maintained at the level to which the relief valve 13 had been reduced by the reversal of motor 14.

Since the successive positions of Fig. 9 are now passed in reverse order, switch 82 is then closed to restore the initial pressure in cylinder 26, and as piston rod 5i continues to move down, the foregoing sequence of operations repeats over and over again until the sheet is iinally drawn to the wrapped position shown by the dot-dash lines of Fig. 2, or to any desired angular position short of a full 90 wrap.

The control function of means i4 will be readily apparent from theforegoing, the same acting to .through pipe I I9.

increase and decrease the pressure inV tension means ,|3nas the latter alternately pays out and maintains its pressure.

It will be realized that when the rod 5| of means I1 has reached its downward position, said rod will rmaintain a pulling force on sheet 9 that has been wrapped. Now, by using said means I'.' to create an increased tension on the sheet, spring-back thereof is obviated.

. Whether stretch-wrap forming over a die of uniform width or over a conical die, as shown in Fig. l, the forces applied to means I3, I4 and Il of the middle bank should be the average of the forces applied to the same means of the outer banks. This is necessary and desired so that jaws |5 are subject to uniform pull along their lengths-although the pull at one end may be greater than that on the other end. In this way, the components of the three banks each. pulls its own weight. The means for this purpose is shown in Fig. 8.

In Fig. 8, the hydraulic units are typical of the-tension means I3, control means I4 and `actuating means I'I ofthe two outer banks of the machine, and hydraulic unit. |0| is typical of the same three means of the middle bank. Pipes |02 are typical of pipes 1|, 'I8 and 30 of the two outer banks, and pipe |03 is typical ofthe same three pipes of the middle bank.

A pressure-dividing valve |04 is provided, the same Vcomprising two cylinders |05 in tandem, each connected to one pipe |02 by a pipe |00, a piston |01 in each cylinder |05, and a single piston rodV |08 connecting said pistons. The dividing valve |04 further includes a cylinder |00, an exhaust connection I I0 between said cylinder and cylinders |05, a piston in cylinder |05, and a piston rod ||2 arranged parallel to piston rod |08. A lever IIShas a fulcrum ||4 that divides the same into arms ||5 Vand ||6 that are engaged by the ends of rods |08 and H2. Arm is half the length of arm IIB. A pressure regulatablerelief valve I |'I is connected by a pipe H8 to pipe |03, and a pressure regulating pipe ||9 extends from cylinder to valve III. The arrow represents the force applied against lever farm l5 and arrow |2| the force transmitted by lever arm I6.

The pressure supplied through pipes |02 to chambers |22 of units |00 enters chambers |23 of cylinders |05 through pipes |06. Whether the same or' different, these two pressures added together create the force I 20 applied by rod |02 to lever arm H5. Since lever IIS has its arms at a one-to-two ratio, the force |2| transmitted by arm |16 to "rod ||2 is one-half the force |20. Although travelling twice the distance that rod `|08 travels, rod I2 exerts a pressure in chamber |24 of cylinder |00 that is half the sum of the pressures in chambers |22 and, therefore, the average of said pressures.

The pressure in chamber |24 is added to the Vspring loading or setting of relief valve Since the relief valve, through pipe |I8,`controls the pressure delivered by pipe |03 to chamber |25 of cylinder IOI, any increase in pilot pressure from chamber |24 will increase the pressure setting of said relief valve to increase the pressure in chamber |25. Any decrease of pilot pressure results in a decrease of pressure in said chamber |25. Therefore, the relief valve, accordingto lpilot pressure from chamber |24, controls the -pressure in unit I0 While the invention that has been illustrated and described is now regarded as the preferred embodiment, the construction is, of course, subject to modifications without departing from the spirit and scope of the invention. It is therefore not desired to restrict the invention to the particular form of construction` illustrated and described, but to cover all modicaticns that may fall within the scope of the appended claims.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. A stretch-wrap forming machine comprising, in combination, a central support for a die over the surface of which a sheet is adapted to be formed, similar oppositely formed means on opposite sides of said support and die to stretch and Wrap said sheet around said die, each said A means comprising a first hydraulic cylinder unit having a piston rod directed toward said central support, a universally pivotal mount for said cylinder unit disposed laterally of said support and die, a second hydraulic cylinder unit pivotally carried on the end of said piston rod and having an extending piston rod, a jaw adapted to grip an edge of the sheet, a pivot connecting said jaw and the latter piston rod, said pivot being transverse to the pivot carrying the second hydraulic cylinder unit, a third hydraulic cylinder unit having an extending piston rod, a universal pivotal mount for the cylinder of the latter unit disposed on the side of the support that is opposite to the die therein, the piston rod of the third cylinder unit extending in a direction to intersect the piston rod of the first cylinder unit, and a universal connection between the piston rods of the first and third cylinder units.V

2. A stretch-wrap forming machine comprising, in combination, a central support for a die overthe surface of which a sheet is adapted to be formed, similar oppositely formed means on opposite sides of said support and die to stretch and wrap said sheet around said die, each said means comprising a first hydraulic cylinder unit having a piston rod directed toward said central support, a universally pivotal mount for said cylinder unit disposed laterally of said support and die, a second hydraulic cylinder unit pivotally carried on the end of said piston r'od and having an extending piston rod, a jaw adapted to grip an edge of the sheet, a pivot connecting said jaw and the latter piston rod, said pivot being transverse to the pivot carrying the second hydraulic cylinder unit, a third hydraulic cylinder unit having an extending piston rod, a universal pivotal mount for the cylinder of the latter unit, and a universal connection between the piston rods of the rst and third cylinder units, the third cylinder unit being disposed at an angle of approximately ninety degrees with respect to the disposition of the rst cylinder unit.

43. A stretch-wrap forming machine according to claim 1: a guideway in which the universal pivotal mount of the third cylinder unit is movable, and means to adjust said mount in said guideway to position the same as desired relative to an edge of a die mounted on the central support.

4. A stretch-wrap forming machine according to claim 1: a guideway in which the universal pivotal mount of the third cylinder unit is movable, and means to adjust said mount in said guideway to position the same as desired relative to an edge of a die mounted on the central support, said latter means comprising a fourth hydraulic cylinder unit disposed laterally of the latter mount and having a piston rod connected to said universal pivotal mount.

5. A stretch-wrap forming machine according to claim l: means carried by the piston rod of the iirst cylinder unit and operatively connected to the pivot that carries the second cylinder unit to move said second unit on said pivot relative to the `first cylinder unit.

6L A stretch-wrap forming machine comprising, in combination, a central support for a die over the surface of which a sheet is adapted to be formed, similar oppositely formed means on the opposite sides of said support and die to stretch and wrap said sheet around said die, each said means comprising a tension-imparting unit provided with a projectable and retractable member directed toward said support, a universally pivotal mount for said unit disposed laterally of said support and die, a tension-controlling unit pivotally carried by said projectable and retractable member and provided with a secondprojectable and retractable member, a jaw adapted to grip an edge of the sheet, a pivot connecting said jaw andl said second projectable and retractable member, said pivot being transverse to the pivot carrying the tensionfcontrolling unit, actuating means comprising a third projectable and retractable member, a universal pivotal'mount for said actuating means disposed on the side of the support that is opposite lto the diethereon, the third prcjectable and retractable member eX- tending in a direction to intersect the projectable and retractable member'of the tension-imparting unit, and a universal connection between the projectable and retractable'members oi the tension-imparting'and actuating units.v

* 7.V A stretch-wrap forming machine according vto claim 6: locating means connected to the universal pivotal mount of the actuating unit to adjust the position of the latter unit relative to an edge of a die on said central support.

, 8. A stretch-wrap forming machine according toclaim 6: means carried by the rst projectable `and yretractable member and operatively connectedV to the pivot of the tension-controlling unit to move the latter unit on said pivot relative to the tension-imparting unit.

9. A stretch-Wrap forming machine according to claim 6: a plurality of tension-imparting, tension-controlling, and actuating units on each side r ofthe central'support and arranged in a plurality of parallel side-by-side banks, the jaw, on each side of the die support, extending in the direction of the longitudinal dimension of the support and in common pivotal connection with the second projectable and retractable members vof the tension-controlling units of said plurality comprising a tension-imparting unit having a projectable and retractable member directed toward said central support, a xed mount including a pivot for said unit for free pivotal movement of the unit in one plane relative to the die, a tension-controlling unit carried on a pivot on said member for pivotal movement of said tension-controlling unit in the same plane relative to said member, said tension-controlling unit also having a projectable and retractable member, a jaw adapted to grip an edge of the sheet, a pivot connecting said jaw and said projectable and retractable Ymember of said tension-controlling unit for movement of said jaw in a plane transverse to the mentioned plane, and actuating means connected to the first projectable and retractable member to exert a pull on the pivot thereof to pivotally move the tension-imparting unit and the tension-controlling unit in said firstmentioned plane and to simultaneously move the jaw in a path around the Vdie on the support and in the same first-mentioned plane.

11. A stretch-wrap forming machine according to claim 10: a plurality of tension-imparting, tension-controlling and actuating units on each side of the central support and arranged in a plurality of parallel side-by-side banks, the jaw on each side of the die support extending in the direction of the longitudinal dimension of the support and in common pivotal connection with the projectable and retractable members of the tension-controlling units of said plurality of banks.

12. A stretch-wrap forming machine according to claim 10: a plurality of tension-imparting, tension-controlling and actuating units on each side of the central support andarranged in a plurality of parallel side-by-side banks, the jaw on each side of the die support extending in the direction of the longitudinal dimension of the support and in common pivotal connection with the projectable and retractable members of the tension-controlling units of said plurality of banks, and a second pivot for the tension-imparting unit transverse to the pivot included in the mentioned mount of the tension-imparting unit and combining with the mount-included pivot to mount said tension-imparting unit to pivotally move in a plane transverse to the first-mentioned plane during angular movement of the jaw in its path around the die on the die support.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,003,127 Vaughn May 28, 1935 2,277,640 Harrington Mar. 24, 1942 2,307,544 Robinson Jan. 5, 1943 2,431,173 Hawkes Nov. 18, 1947 2,437,092 Greene Mar. 2, 1948 2,459,132 Nielsen Jan. 11, 1949 2,515,734 Rathgen July 18, 1950 2,553,092 Hubbert May 15, 1951 2,558,071 Castle June 26, 1951 2,632,493 Gray Mar. 24, 1953 

